Missing Texture Color
The color, that is used when a texture is not found, is defined by four macros in util_texture.h. The color is magenta with full alpha (no transparency).

#define TEX_IMAGE_MISSING_R 1
#define TEX_IMAGE_MISSING_G 0
#define TEX_IMAGE_MISSING_B 1
#define TEX_IMAGE_MISSING_A 1


Code is licensed under GPLv3

The macros are used whenever image data isn't available, e.g. in ImageManager::device_load_image() image.cpp when the loading of an image failed or in ImageTextureNode::compile() nodes.cpp when no texture has been selected in the Image Texture node.